1. Field of the Invention
The present invention relates generally to an apparatus and a method of multiple decoding, and more specifically, to apparatuses and methods of reproducing a plurality of data designated from one MPEG (Moving Picture Experts Group) transport stream composed of a plurality of encoded data.
2. Description of the Background Art
In recent years, satellite television broadcasting, cable television broadcasting and ground wave television broadcasting have been digitized, so that a broadcasting station can transmit a plurality of video and audio data. In a receiver, it is possible to receive the plurality of video and audio data, and selectively display by video and output by audio any of the data. That is, a user can select and view any one of a plurality of video and audio transmitted by the broadcasting station.
A conventional decoder used in such a receiver will be described with reference to FIGS. 7 to 9.
FIG. 7 is a block diagram showing the configuration of a conventional decoding apparatus. FIG. 8 is a diagram showing a specific example in which data representing video and audio and other data are multiplexed on an MPEG transport stream. FIG. 9 is a flow chart for explaining processing performed by the conventional decoding apparatus.
As is well known, the MPEG transport stream is a stream data string in a data format defined in the ISO/IEC13818-1 standard for data transmission and receiving, and is composed of units called packets. On the side of a transmitter, data representing a plurality of video and audio and other data are respectively stored in payload portions of the packets, and the packets are then multiplexed, to compose an MPEG transport stream (FIG. 8) for transmission toward a receiver. On the other hand, on the side of the receiver, it is possible to judge a header portion of each of the packets composing the MPEG transport stream, to selectively obtain the data representing video and audio and other data.
The conventional decoding apparatus receives the MPEG transport stream including encoded data representing a plurality of video and audio. A method of selecting the inputted MPEG transport stream is not required in describing the background art. Further, modulation and demodulation control is performed depending on a satellite, a cable, and a ground wave and hence, the description thereof is omitted herein. Consequently, the following description will be made using as a premise a state where the corresponding MPEG transport stream has already been selected.
In FIG. 7, the conventional decoding apparatus comprises a data extractor 701, a buffer 702, a decoder 703, a buffer manager 704, a decoding controller 705, and a reproduction controller 706.
First, the reproduction controller 706 instructs the decoding controller 705 to start decoding (step S901). The decoding controller 705 which has received the instruction instructs the decoder 703 to start decoding (step S902), and instructs the buffer manager 704 to start data input to the buffer 702 (step S903). The reproduction controller 706 then instructs the data extractor 701 to extract a packet having desired header information from the inputted MPEG transport stream (FIG. 8), the packet having “Header 1” in its header portion in this example (step S904).
When the extraction instruction is issued to the data extractor 701, the input of the MPEG transport stream externally supplied to the data extractor 701 is started (step S905). The data extractor 701 sequentially extracts the packets each having “Header 1” designated from the MPEG transport stream, and stores in the buffer 702 the data stored in the payload portions of the extracted packets (step S906). The decoder 703 obtains the data stored in the buffer 702, and sequentially performs the decoding (step S907). The decoder 703 confirms whether or not the decoded data, corresponding to a predetermined unit to be outputted, is ready for output (step S908). The predetermined unit to be outputted is a frame in the case of video data, for example. In the confirmation in the step S908, when the decoded data, corresponding to the predetermined unit, are not ready for output yet, the decoder 703 continues the decoding of the subsequent data (steps S905 to S907) to wait for data. When the decoded data, corresponding to the predetermined unit, are ready for output, the decoder 703 outputs the decoded data in the predetermined unit (step S909).
In the above-mentioned decoding apparatus, however, only one of the encoded data representing video and audio existing in the one MPEG transport stream can be decoded and reproduced.
Also, in the conventional decoding apparatus, there exists no method of sufficiently correcting any error which has occurred at the time of broadcasting from a broadcasting station or in a transmission path.